Knife for cutting lumber



P. A. KIRSTEN KNIFE FOR CUTTING LUMBER 'Dec. 3, 1968 4 Sheets-Sheet 1Filed Aug. 26, 1965 1958 P. A. KIRSTEN KNIFE FOR CUTTING LUMBER FiledAug. 26, 196' r 4 Sheets-Sheet 2 Inventor- Dec. 3, 1968 P. A. KIRSTEN3,414,029

KNIFE FOR CUTTING LUMBER Filed Aug. 26, 1965 4 Sheets-Sheet 5 Fig.5

Dec. 3, 1968 P. A. KIRSTEN $414,029

KNIFE FOR CUTTING LUMBER Filed Aug. 26, 1965 4 Sheets-Sheet 4 InventorUnited States Patent Office 3,414,029 KNIFE FOR CUTTING LUMBER PaulArthur Kirsten, Ernst-Moritz-Arndt-Str. 6, Renal, near Bonn, GermanyFiled Aug. 26, 1965, Ser. No. 482,850 8 Claims. (Cl. 144-230) ABSTRACTOF THE DISCLOSURE A knife for use with wood cutting machines to cutstrips and shavings of predetermined width comprising a body memberhaving a bottom chip surface and a forward edge surface defined by apair of planar surface portions disposed in parallel relation to thelongitudinal axis of the knife. A plurality of parallel spaced recessesare formed in the chip surface transverse to the longitudinal axis ofthe body member and intersect the forward edge surface to define cuttingedges therewith. The spaced recesses define splitting tips therebetweenwhich determine the widths of the strips cut. The planar surface portionof the forward edge surface adjacent the chip surface includes thecutting edges and is disposed in co-planar relation with the cuttingplane of'the knife, while the other planar surface portion is angularlydisposed relative to the cutting plane to form a relief angletherebetween.

The present invention relates to an improved form of cutting knife whichis particularly advantageous when used in conjunction with a disc typewood cutting machine or a cylindrical type wood cutting machine.

In the cutting of lumber in order to produce flat shavings forcellulose, veneer panels or the like, splitting and peeling knives areused whereby two cutting dimensions of the resultant wood shavings aredetermined. That is, the length of a wood shaving in the direction ofthe wood fibre is determined by the length of the splitting knives, andthe thickness of such shavings is determined by the distance between thepeeling knife cutting edge and the surface of the knife carrier memberagainst which the wood engages. The influence of the pressure by whichthe wood is engaged against the knife carrier is not a significantfactor with respect to the thickness of the wood shavings produced.

It is known in the art that the splitting knives can be eliminated byusing disengaged peeling knives whereby the partial cutting edges of thepreceding peeling knife are placed on the gaps of the subsequent knife.In the area of the knife gaps the shaving groove located ahead of theknife is interrupted by bridges for supporting the wood. However, with nknives of this type only the production of 11/2 solid knives isobtained. Released or disengaged peeling knives are also known whereboth the tooth (outer cutting circle) and the gap (inner cutting circle)are effective as peeling knives. The fact that long splinters are torninto the shaving grooves is a disadvantage in tool carriers having thistype of knife, and bridges for supporting the wood cannot be utilized insuch a case. If such a knife were positioned obliquely and if the slotahead of the knife which directs the shavings into a shaving-receivingarea were bridged by the length of the shaving in the direction of thefibre, poor cutting conditions would result for the splitting, becauseat the trailing end of the cutting edge a negative cutting angle exists.The wood fibres would not be cut through smoothly at such a location,but rather such fibres would be torn or crushed off. This disadvantagewould also exist with obliquely positioned knives having rectangularrecesses over their width on the side of the shaving surface.

It is also known in the art to provide knives where an open space isground out in a sawtooth-like manner.

3,414,029 Patented Dec. 3, 1968 The tooth tips in such a case willcontrol the splitting under favorable conditions, but such knives willnot cut flat shavings parallel to the wood fibre. In order to providefor cutting parallel to the wood fibre with knives of the latter type,it has been proposed to feed the wood at such an angle that the fibresof the wood are parallel to the partial cutting edges of the knives,rather than to feed the wood so that it is parallel to the axis of theknife carrier member. There is a tendency for the wood to be milled outin a rack-like manner, and therefore each individual piece of woodplaced in the machine must be maintained in a firm manner and must befed at a predetermined speed in the longitudinal direction. The piecesof wood may have only a small diameter, since otherwise the shaft of theknife tends to become unduly long.

In addition to the foregoing, it is known to provide peeling kniveshaving recesses over the width of the shaping surface. That is, recessesare provided over the width of the surface of the knife which forms thecutting angle gamma with the line perpendicular to the cutting directionof the cutting edge. Thus, splitting cutting edges are reduced. In orderto achieve uniform thicknesses of the Wood shavings, the knife should beoperated without any clearance angle. However, it has been found thatsuch knives will not operate satisfactorily because considerabledifficulty is encountered where too small a clearance angle is providedsince the exposed surface becomes smeared with wood resin causinggeneration of heat, and the surface of the knife carrier also becomessmeared making cutting extremely difiicult. Apart from the knvies lastabove mentioned which are not at all satisfactory for the reasonsstated, all other known knives discussed hereinabove leave tracks witheach cut on the wood. The splitting knives are placed slightly above thecutting plane of the peeling knives in the case of excelsior machines orcutters of flat discs, or they are placed above the cutting cylinder incutting machines having cylindrical type knife carriers, and in suchinstances the splitting knives leaves splitting indentations on thesurface of the material from which shavings are being cut. Released ordisengaged peeling knives and those with sawtooth-like cutting edgesleave depressions corresponding to the length of the shaving or theywill mill out the wood in a rack-like manner. During the succeeding cut,the corresponding knives do not always hit the same tracks again becausethe wood to be cut, particularly during the final phase of the cuttingoperation, can no longer be guided and held firmly enough, and theresult is that undesirably small and fine parts are produced.

It should also be noted that certain disadvantages occur during thegrinding of released or disengaged knives whose teeth split on an outercutting circle and peel thereon, and whose gaps peel on an inner cuttingcircle. Such knives are always sharpened on a special machine inaccordance with a plunge-cut method to produce a released cutting edge.Often unduly pronounced round surfaces are produced which cause crushingof the shavings and also increase the contents in fines, In order toeliminate such disadvantages, the invention provides that at a giventhickness of the shavings to be produced, the depth of the recesses atthe shaving surface of the knife is made a function of the shavingthickness, and each partial cutting edge formed by such recessespossesses at least one special exposed surface comprised of one or moreparts. This exposed surface may be formed according to the invention byat least two partial exposed surfaces of various inclinations whereby incertain cases one of these partial cutting surfaces may he provided witha zero clearance angle alpha as a final grinding phase. The use of aknife of the present invention is particularly advantageous withcylindrical knife carriers because in such a situation the knife isdisposed parallel to the axis of the carrier member and its partialcutting edges produce oblique cuts with respect to the direction of thewood fibres, so that the wood is fed parallel to the knife carrier axis.

Now in order to acquaint those skilled in the art with the manner ofutilizing and practicing my invention, I shall describe in conjunctionwith the accompanying drawings certain preferred embodiments of theinvention.

In the drawings:

FIGURE 1 is a front elevational view of a disc type wood cutting machineequipped with knives constructed in accordance with the presentinvention;

FIGURE 2 is a side elevational view of the apparatus of FIGURE 1;

FIGURE 3 is an enlarged fragmentary front elevational view of a cuttingknife formed in accordance with the present invention;

FIGURE 4 is a sectional view taken along the line A-B of FIGURE 3;

FIGURE 5 is a front elevational view of an alternative embodiment of thepresent invention showing a cylindrical type wood cutting machineequipped with knives constructed in accordance with the invention;

FIGURE 6 is a top plan view of the apparatus of FIG- URE 5;

FIGURE 7 is an enlarged fragmentary sectional view showing the mountingof a knife on the cylindrical knife carrier of FIGURE 5; and

FIGURE 8 is a fragmentary top plan view of the apparatus of FIGURE 7.

Referring now to the drawings, FIGURES 1 and 2 show a disc type woodcutting machine having a plurality of knives 1 which are fixedly securedto a knife carrying disc 4. The knife disc 4 is rotated by a motor androtates about an axis 55. The wood 6 to be chipped is fed by a feedingmember 7 against a front surface 8 of the knife disc 4, and the wood isdisposed on the bottom of a compartment 9 which extends closely adjacentto the cutting surface of the knife 1.

Referring to FIGURES 3 and 4, a knife 1 is shown clamped in fixedposition to the disc 4 by means of a clamping iron 3 and a screw 2. Thecutting edges of the knife, explained more fully hereinbelow, projectoutwardly of the front surface 8 of the disc 4 through an appropriateopening defined by edge portions 20 and 20'. The cutting edges rotate ina cutting plane 10-10 and peel or cut shavings having a thickness d inplanes parallel to the fibers of the wood 6.

Each knife 1 comprises a body member having a rectangular configuration,as viewed in FIGURE 1, with the longitudinal axis of the body memberbeing disposed in generally radial relation to the axis of rotation 5-5of the disc 4. The knife body member has a bottom chip surface 11 and anupper surface 11 parallel to the bottom chip surface. The knife bodymember also has a forward edge surface defined by a generally planarfirst surface portion 13' and a second planar surface portion 15. Thefirst and second planar surface portions 13 and 15, respectively, aredisposed in parallel relation to the longitudinal axis of the bodymember, with the first surface portion 13 preferably being co-planarwith the cutting plane 10-10. The second planar surface portion ispreferable angularly disposed relative to the plane of the chip surface11 so as to define a relief angle alpha between the second planarsurface and the cutting plane during cutting operation. The relief anglealpha is provided to minimize the area of the forward edge surface ofthe knife which lies in the cutting plane 1010, thereby reducing thefriction surface between the knife and the material being cut.

The bottom chip surface 11 has a plurality of parallel spaced recesses12 formed therein, such as by milling, which recesses extend intransverse relation to the longitudinal axis of the knife body member.Referring to FIG- URE 3, each recess 12 is defined by a first wallportion disposed in substantially normal relation to the bottom chipsurface 11 and a second wall portion disposed in oblique relation to theplane of the chip surface and intersecting the first wall portion at 14.The cross sectional area of each recess 12 is generally triangular inshape when considered within the envelope defined by the first andsecond wall portions and the plane of the chip surface 11. Preferable,the depth of each recess 12, as measured by the height of the first wallportion normal to the bottom chip surface 11, is substantially equal tothe thickness d of the strips or shavings to be cut from the wood 6. Thefirst and second wall portions intersect the planar surface portion 13of the forward edge surface of the body member so as to define andestablish cutting edges at the lines of intersection. The cutting edgesof each knife 1 are thus within planar surface portion 13' and definecutting plane 1010 during operation of the cutting machine.

The parallel recesses 12 define splitting tips 13 there between, whichsplitting tips are spaced a distance 1 equal to the desired width ofstrips or shavings cut from Wood 6. The portions of the splitting tips13 adjacent the planar surface portion 13' serve to cut the strips orshavings transversely to the direction of the fibers of wood 6 and thusdetermine the widths of the strips cut by the aforedescribed cuttingedges of the knife.

By establishing the cutting edges of each knife 1 in the plane of planarsurface 13', it can be seen that grinding of the knives 1 to maintainsharp cutting edges can be readily accomplished by one normal grindingoperation over the entire longitudinal length of surface 13. Also theplanar surface 15 forming the relief angle alpha with the cutting plane10-10 can be readily ground to the desired relief angle through acontinuous grinding stroke in the longitudinal direction of the knife.

-.If flat wood chips having a thickness of approximately 3 mm. are to bepeeled, it may be desirable to reduce the surface area of the planarsurface 13' which engages the wood 6 in frictional sliding relation.Such a reduction may be desirable where the frictional sliding surfacecreates excessive heat during cutting which may damage the cutter knifeor reduce the life of the cutting edges. The exposed surface area 13'may be readily reduced by a grinding wheel 16 moved against the knife 1adjacent the cutting edges defined by the oblique wall portions ofrecesses 12. Noting FIGURE 3, the grinding wheel 16 can be caused toremove a portion of the knife 1 to produce a relief surface 13, 17, 18,19 generally adjacent each of theoblique cutting edges with the reliefsurface so produced being angularly inclined relative to said bottomchip surface and the longitudinal axis of the body member. Itwill beunderstood that the amount the exposed surface area 13 is reduced willbe determined by the depth of cut of grinding wheel 16 as viewed inFIGURE 4. After lifting the grinding disc 16, the knife 1 is displacedby an amount equal to the length of the wood shavings 1 in thelongitudinal direction, after which the next surface 13, 17, 18 isground and so on. In order to limit the steps in the longitudinaldirection of the knife, the surface 13-14 extending over the entirewidth of the knife may be utilized. The operation is somewhat similar tothat used for the sharpening of saws, and the surfaces 13, 17, 18, 19are somewhat inclined in their longitudinal direction against thecontinuous exposed surface 15. The grinding widths 13-17 and 18-19 neednot be precise, as is the case in connection with plunge-cut grindingfor released knives. That is, even slightly rounded edges on thegrinding wheel will not have any detrimental effect. Subsequent to thesharpening operations at the exposed surfaces 15 and 13, 17, 18, 19, afine grinding is effected in the plane 10-10 with the result that allpartial cutting edges are placed precisely in the cutting plane 1010.

It is also possible without difliculty to impart upon the grinding disc16 a width equal to the partial cutting edge length and to extend thepartial exposed surfaces 13, 14, 18, 19, so produced beyond the edge 20.While such an operation comprises a plunge-cut grinding operation, it isnot at such a location as to incur the disadvantages discussedhereinabove, because slight roundings as a result of a somewhat roundedgrinding wheel disc will not be located at the cutting edges but ratherin the exposed surface area. A subsequent fine grinding to produce aphase located in the cutting plane 10 will produce a veryuseful knife inaccordance with the present invention.

FIGURES 5 and 6 show an alternative embodiment where the knives 1 of thepresent invention are utilized in conjunction with a cylindrical typewood cutting machine. In this instance the knives 1 are secured to acylindrical knife carrier member 4 which is rotated by means of a motorand a clutch 50 around an axis 5. The wood 6 to be chipped is advancedby a feeding member 7' against the supporting surface 8'. Accordingly,the wood is situated at the bottom of a supporting compartment 9' whichextends closely adjacent to the cutting edges of the knives 1.

FIGURES 7 and 8 illustrate a knife 1 which is secured by means of ascrew 2 and a clamping iron 3 in order to fasten the knife to the knifecarrier member 4. The cutting edges of the knives rotate in a cuttingcylinder 1010' and peel shavings of a thickness d parallel to the woodfibre.

When used in conjunction with cylindrical knife carrier members, theknife of the present invention provides the additional advantage that ata corresponding depth t of the recesses 12 in the cutting surface 11 ofthe knife 1, as shown in FIGURE 8, the partial cutting edges 13-14formed thereby assume a sloping or inclined position relative to theaxis of the knife carrier member 4 so that even where the knife 1 isitself parallel to the axis there will be provided an oblique cutinclined at the usual angle delta to the direction of the wood fibre InFIGURE 8, the chip length of the wood in the fibre direction asindicated at l is equal to 25 mm., and the depth of the recesses 12 atthe chipping surface of the knife as indicated at t is equal to 8 mm.The partial cutting edges 13-14 are thus provided with an obliqueposition to the axis of the knife carrier member, the angle therebetweenbeing about 18 degrees, the latter being a mean value of the usualoblique cutting angles, The knife 1 is itself oriented parallel to theaxis of the knife carrier as shown in FIG- URE 8 where the knife edge2020 extends parallel to the axis 5'5'. The knife of the presentinvention may also be used in excelsior machines.

While I have described my invention in certain preferred forms, I do notintend to be limited to such forms except insofar as the appended claimsare so limited, since modifications coming within the scope of myinvention will readily occur to others, particularly with my disclosurebefore them.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

I claim:

1. A knife for use with wood cutting machines and the like to cut stripsand shavings of predetermined width, comprising, a body member having abottom chip surface and a forward edge surface, said bottom chip surfacehaving a plurality of recesses formed in spaced relation therein, eachof said recesses being defined by a first wall portion and a second wallportion intersecting said first wall portion, said first and second wallportions intersecting said forward edge surface so as to define cuttingedges at the lines of intersection therewith, said spaced recessesdefining splitting tips therebetween, said splitting tips being spacedapart a distance equal to the desired width of the strips to be cut bythe knife, said forward edge surface having a generally planar firstsurface portion including said cutting edges and disposed in parallelrelation to the longitudinal axis of said body member, and said forwardedge surface further having a second planar surface portion angularlydisposed relative to the plane of said chip surface so as to define arelief angle between said second surface portion and the cutting planeduring cutting operation.

2. A knife in accordance with claim 1 wherein said first wall portion isdisposed in substantially normal relation to said bottom chip surfaceand said second wall portion is disposed in oblique relation to saidchip surface.

3. A knife in accordance with claim 1 wherein the depth of each of saidrecesses, when considered in said first planar surface portion of saidforward end surface, is approximately equal to the predeterminedthickness of the strips to be cut during cutting operation of the knife.

4. A knife in accordance with claim 1 wherein said first planar surfaceportion including said cutting edges is disposed in co-planar relationwith the cutting plane of the knife during cutting operation thereof.

5. A knife in accordance with claim 1 wherein said first and secondplanar surface portions of said forward edge surface extendsubstantially the full longitudinal length of said body member.

6. A knife in accordance with claim 1 wherein said first and second wallportions define generally triangular cross sectional configurations whenconsidered with the plane of said bottom chip surface.

7. A knife as defined in claim 6 wherein said recesses extend inparallel relation to each other transversely to the longitudinal axis ofsaid body member.

8. A knife in accordance with claim 1 wherein said first planar surfaceportion of said forward edge surface is adapted for co-planar relationwith the cutting plane of the knife during cutting operation thereof,and wherein said forward edge surface further includes a relief surfacegenerally adjacent each of said cutting edges defined by said secondwall portions intersecting said forward edge surface, said reliefsurfaces being angularly inclined relative to said bottom chip surfaceand the longitudinal axis of said body member.

References Cited UNITED STATES PATENTS 1,436,208 11/1922 Sprague 241240FOREIGN PATENTS 715,294 9/1954 Great Britain. 964,827 5/ 1957 Germany.1,166,960 6/1958 France.

FRANCIS S. HUSAR, Primary Examiner.

